Condenser used in zinc production



Aug. 2s, 1956 s. RQBSON ETAL 2,760,770

' CONDENSER USED IN ZINC PRODUCTION /m/enfor@ STANLEY ROBSON AND yLESLIE JACK DERHAM Aira/6x15 Aug. 28, 1956 s. RoBsoN ET Al. 2,760,770

coNDENsER USED 1N ZINC PRODUCTION Filed July 29, 1953. 7' sheets-sheet 2llave/)fors STANLEY ROBSON AND y LESLIE JACK DERHAM Aug. 28, 1956 s.RoBsoN ET AL 2,760,770

coNDENsER USED IN ZINC PRODUCTION Filed July 29, 1953 7 Sheets-Sheet 3 f/WMSQNLEY ROBSON AND LESLIE JACK DERHAM y Afforneys S. ROBSON ET ALCONDENSER USED IN ZINC PRODUCTION 7 Sheets-Sheet 4 Aug. 28, 1956 FiledJuly 29, 1953 F/ G. 7. 50 67 44 67 45 66 46 f /nvenfor' STN LESLfforneys Aug. 28, 1956 s. RoBsoN ETAL 2,760,770

coNDENsER USED IN ZINC PRODUCTION 7 Sheets-Sheet 5 Filed July 29, 1955 Aff'a /we ys Aug. 28, 1956 s. RoBsoN ETAL 2,760,770

coNnENsER USED IN zINc PRODUCTION Filed July 29, 195sq 7 sneaks-sheet eAug.28, 1956 s. ROBSON ETA'. 2,760,770

CONDENSER USED IN ZINC PRODUCTION Filed July 29, 1953 7 Sheets-Sheet 7 Osa 50a. ssfkuw i4 59 b 8 A I f I mm i /nwmrs EY ROBSON AND 5), LESLIEJACK DERHAM Afro/'ners United States Patent CONDENSER USED 1N ZIN CPRODUCTION Original application March 11, 1949, Serial No'. 80,916,

now Patent No. 2,671,725, dated March 9, 1954. Di-

and this application `l'uly 29, 1953, Serial No.- 3 41 17 Claims. (Cl.Z66-15) This application is a division of application 80,916 filed March11, 1949, now Patent 2,671,725, granted March 9, 1954.

This invention relates to the production of zinc and has v for itsobject improvements in the methodof and apparatus for producing zinc.The invention relates more particularly to the recovery of zinc from abody of molten lead that has `been used as a condensing medium for zincvapor obtained in zinc smelting operations.

Prior proposals to use molten lead as a condensing medium for zinc vaporobtained in smelting operations have not met with much favor. One of themain reasons, of course, is the cost of the large amount of lead thatmust be employed. Another is the difficulty of recovering the smallamount of zinc from the large amount of lead in a satisfactory manner.In view particularly of renewed efforts to find a way commercially tosmelt zinc bearing materials in a blast furnace, attention is againdirected to the possibility of using molten lead as a condensingr mediumfor zinc vapor.

Gaseous mixtures containing zinc vapor, carbon monoxide, and asubstantial amount of carbon dioxide are especially difficult to treatin a zinc condensing operation ecause of the tendency of the carbondioxide to react with the zinc to ferm an objectionable amount of thezinc oxide. The following composition is typical of the gaseous mixturesderived from blast-furnace smelting of zinc-bearing ores, residues orthe like:

Percent by volume Zinc-bearing gaseous mixtures of similar type can alsobe derived from the electro-thermic smelting of zinc, but in this casethe zinc content is usually rather higher and the CO2 content may berather less.

A method of condensing and recovering the zinc values from a gaseousmixture of the type referred to is disclosed in our co-pendingapplication Serial No. y535,290 led May l2, 1944, now Patent No.2,464,262 issued March 15, 1949, of which the present application is acontinuation-impart. The method of condensing comprises bringing thegaseous mixture while still hot into intimate shock-chilling contactwith circulating molten lead in a condensing zone maintained at atemperature not greater than 550 C. to cause the gaseous mixture to coolto a temperature below that at which the carbon dioxide can react withthe zinc to form objectionable zinc oxide, condensing the zinc vapor inthe lead and accumulating a body of the solution.

The method of recovering the condensed zinc comprises cooling the lowerportion of the body` of lead-zinc solution to a temperature below 418C., but not below 2,760,770 Patented Aug. 28, 1956 the meltingl point oflead, to precipitate zinc therefrom while maintaining the upper portionof the body of the solution'fabove 418 C., permitting the precipitatedzinc to rise into the upper portion of the body of solutionA with theresultant remelting of the Zinc and the formation of a supernatant layerof molten Zinc, removing molten zinc from this supernatant layer andreturning the molten lead from which the zinc was precipitated' forre-use in the condensing step.

While this method of recovering condensed zinc from molten lead hasgiven excellent results, we have found that when the lower portion ofthe lead-zinc solution isv cooled to a temperature aslow as 418 C., someof the precipitated zinc crystals tend to adhere to the sides of thevessel in which they are precipitated. Unless scraped from the sides ofthe vessel, the crystals tend to buildI up and thus to insulate thevessel. To this extent, at least, the method is a drawback and leavessomething to be desired.

Investigation conrmsour discovery that zinc may be recovered from moltenlead used as a condensing medium for zinc vapor and that drawbacks ofthe type mentioned may be avoided, while at the same time gainingcertain other operating advantages.

In accordance wth the method of the invention for recovering zinc from abody of molten lead used in a condensing zone as a condensing medium forzinc vapor obtained in a smelting operation, the condensation of Zinc'vapor is continued until the zinc content of the molten lead builds upto a point corresponding to the saturation point of the lead for zinc ata temperature above the freeze ing point of the Zinc but below thetemperature of the lead in the condensing Zone. The resulting lead-zincsolution is accumulated in a substantially quiescent body. The body ofmolten lead-zinc solution is cooled to a temperature above thefreezingpoint of the zinc but at which dissolved Zinc separates andrises to the top of the body of solution to form a supernatant layer ofmolten zinc and an underlying layer of molten lead. The supernatantlayer of molten zinc is separated atleast in part from the underlyinglayer of molten lead and solution containing the remaining molten leadis returned to the condensing zone for re-use in the condensing step.

Since the lead-Zinc solution from the condensing zone is not cooled lowenough to permit zinc crystals to precipitate, the molten zinc remainslin solution in the molten lead. The temperature drop, however, issutiicient to cause molten zinc in solution to separate, in eiect, andrise as such to the top of the body of solution. Since Zinc has a lowerspecific gravity than lead, the molten zinc rises to the top while themolten lead settles to the bottom. The molten zinc at the top may bedrawn oif readily, and thus be recovered separately from the lead.

For a specific application of the method of the invention, reference mayagain be made to our prior method of recovering condensed zinc frommolten lead, described above and as disclosed in our copendingapplication. Instead of cooling the lead-zinc solutionto such a lowtemperature as 418 C., the temperature is kept above 418 C., andprecipitation of zinc crystals is avoided. In this connection, we foundthat if the body of molten lead coming from the condensing Zone issaturated with zinc at the temperature at which the condensation isleffected, any subsequent cooling of it will cause molten zinc toseparate, or rather a molten solution of zinc-rich alloy whose leadcontent is very small and may be ignored; since further treatment willin any case be necessary if a high purity Zinc is ultimately required.

Therefore, in accordance with the present invention,

the condensation of zinc vapor in the circulating molten lead iscontinued until the zinc content of the molten.

lead exceeds at least 1.7% by Weight; the lead-Zinc solution is thenaccumulated in a substantially quiescent body which is allowed to coolsufficiently to permit some of the zinc dissolved therein to separateand rise as such to the top of the body of solution to form asupernatant layer of molten zinc and an underlying iayer of molten lead,the supernatant layer of molten zinc being then separated, at least inpart, from the underlying layer of molten lead and the solutioncontaining the remaining molten lead being returned to the condensingzone for re-use in the condensing step.

Preferably the resultant lead-zinc solution is accumulated in a coolingzone removed from the condensing zone and the body of solution is cooledto a temperature below 500 C., but above the freezing point of zinc tofacilitate the formation of the supernatant layer of molten zinc.

The necessity for recirculating the lead until the dissolved zinccontent exceeds at least 1.7% arises from the fact, which can beveriiied from the phase diagram of the binary lead-Zinc system, that attemperatures exceeding 418 C. the lead-rich component of the liquidphase contains 1.7 and upwards of zinc; hence, unless the total zinccontent exceeds 1.7%, the zinc-rich component from which alone the zincvalues can be recovered, will not be present at all.

The circulation of molten lead in the condensing zone by means of whichthe condensation of zinc from the gaseous mixture derived from theblast-furnace or other smelting apparatus is effected may be produced bymeans of a rotary paddle wheel or the like device operating in anenclosed condensing chamber and dipping into a pool of molten lead so asto produce a shower of molten lead through which the gaseous mixturederived from the smelting zone is compelled to pass, the molten leadbeing continuously withdrawn from the pool for transfer to the recoveryzone, and the pool replenished with lead from which a part at least ofthe zinc values have been extracted.

The rotary paddle wheel may be replaced by an oscillating paddle or by ahelical type rotor rotating on a vertical axis or by any otherconvenient device for showering the molten lead.

The condensing chamber is preferably arranged as close as possible tothe outlet of the blast-furnace or other smelting apparatus so that thegaseous mixture issuing from the smelting zone reaches the condensingzone without any substantial loss of temperature. This is important,because the gases leave the smelting zone at a temperature not very muchabove the equilibrium temperature of the reaction between zinc vapour,carbon dioxide, carbon monoxide and zinc oxide, having regard to thecomposition of the gases usually encountered. The reaction is symbolizedby At temperatures below the equilibrium temperature the reactionproceeds from left to right. The equilibrium temperature of thisreaction increases as the CO2 content of the gases is increasedrelatively to their other content', and the CO2 content of the gasesfrom a blastfurnace in particular, or, in some instances, from anelectro-thermic furnace, is sufficiently high in relation to the contentof zinc vapour and CO to raise the equilibrium temperature to a valuenot far short of that at which the gases leave the smelting zone, sothat a relatively small drop of temperature between the smelting andcondensing zones will be suihcient to reverse the reactionabovementioned and cause the formation of objectionable zinc oxide.

The recovery zone comprises essentially a vessel into which thezinc-lead solution is delivered from the condensing zone and which isprovided with means'for withdrawing the supernatant layer of molten zincor rather zinc-rich alloy from the top, and means for tapping thepartially de-zinced molten lead from the bottom for return to thecondensing zone. Suitable means may be provided for maintaining thisvessel at the correct temperature.

The invention further contemplates a modification of the condensationstep of the process in which the condensation is carried out in twostages with counterow of the molten lead and gaseous mixture, thecondenser being modified by subdividing it into two compartments, eachcontaining a paddle-wheel or like showering device. The gaseous mixtureis introduced into the compartment next the zinc-vapour producingcomponent and transferred thence through an opening in the partitionseparating the compartments to the more remote compartment from which itis finally exhausted; and molten lead is introduced into the compartmentremote from the zinc-vapour producer and withdrawn from the othercompartment into which it ows via a connecting passage.

We have found that when operating with two-stage condensation in thismanner, the former upper limitation of 550 C. on the temperature of thecondensing Zone can be relaxed as far as concerns the rst stage ofcondensation in the compartment next the zinc-vapour producer, in whichthe temperature may rise to 600 C. or even 620 C., the second stage ofcondensation being conducted so that the rise of temperature of the leadtherein is slight, the temperature of the lead leaving this stage beingpreferably below 500 C. and in any case no greater than 550 C.

Our experiments show that when two-stage condensation is employed inthis manner the zinc-vapour-bearing gases are adequately shock-chilledin the first stage of condensation, and furthermore that dross formationin the condenser is minimised by keeping the temperature of the firststage of condensation above 550 C. and preferably up to about 600 C.

An embodiment of an apparatus suitable for the performance of the methodof the invention is diagrammatically illustrated in the accompanyingdrawings, of which- Figure l is a view, somewhat schematic, in sideelevation of a zinc smelting and recovery plant, comprising a blastfurnace and twin condenser assemblies including zinc-recovery apparatus,partly sectioned on the line l-l of Figure 2;

Figure 2 is a plan view, also somewhat schematic of the plant partlysectioned on the line 2--2 of Figure l;

Figure 3 is a somewhat schematic View in end elevation of the plant;

Figure 4 is a detail view in section on the line 4-4 of of Figures l and3;

Figure 5 is an enlarged detail View in section on the line 5-5 of Figure2;

Figure 6 is an enlarged detail view in section on the line 6--6 ofFigures l and 2;

Figure 7 is a central vertical section of the zinc-separating componenton the line 7-7 of Figures 9 and l0;

Figure 8 is a central vertical section of the Zinc-separating componenton the line S- of Figures 9 and l0;

Figure 9 is a plan of the zinc-separating component;

Figure l0 is a section on the line 10-10 of Figures 7 and 8; and

Figures 1l and l2 are partial views, similar to Figures l and 2,respectively, illustrating a modified arrangement.

The zinc smelting plant illustrated in Figures l to 3. comprises a blastfurnace ll, twin condensers 12, zincseparators i3, and zinc-collectorsi4. The blast furnace gases containing nitrogen, carbon monoxide, carbondioxide and zinc-vapour pass from the blast furnace into each condenserthrough an outlet l5 and a downwardly extending passage lo beneath ahanging wallY 17. Y The interior of each condenser l2, is subdividedinto two cornpartments il@ and 19 by means of a partition 20 in which isan opening 2l. ln the compartment 18 is disposed a horizontal rotor 22,having buckets or pockets, formed in its circumference as shown inFigure 1. A similar rotor 23 is disposed in the compartment 19. Beneaththe rotors 22, 23 respectively are sumps '24, 25. The rotors arerevolved in the direction indicated by arrows in Figure 1 by mechanicalmeans (not shown) situated outside the condenser.

The condenser 12 terminates at the end remote from the blast furnace 11,in an outlet 26 communicating with an uptake 27 from which extends ladownwardly sloping pipe 23 (see Figure 3) communicating with agas-cleaning apparatus (not shown). From the top of the uptake 27extends a stack 29 which is normally shut oi from the uptake by means ofa damper 30 shown in Figure 4 in the closed position by full lines andin the open position by dotted lines.

The compartments 1S, 19 are connected at the bottom by a passage 31 (seealso Figure 6). The base of the condenser is built up alongside thelpartition 2t), inside the compartment 18 and in the built up part isprovided a shallow transverse trough 32 (see also Figure 6), the wallsof which are of unequal height, the wall forming the lower edge `of theopening 21 being higher than the other. At the end remote from thepassage Sil the floor of the Itrough 32 is sloped downwards to enablethe trough to communicate through an opening 33 in the wall of thecondenser with an external well, 34, the upper edge of the opening 33being below the floor of the horizontal `part of the trough 32. From theupper lpart of thewell 34 a trough 35 (see also Figure 5), communicatingwith the well through an opening 36 in its floor, leads to the Zincseparator 13. The well 34 and trough 35' are covered with a refractoryroof, but for convenience'of reading the drawings the roof is not shown.In the bottom of the wall of the compartment 19 of the condenser is 'an`opening 37 from which extends a pipe 3S communicating with the pipe 59of the zinc-separator 13, hereinafter described.

The zinc-separator l1.3 (Figure 7) comprises a cylindrical shell 39 `ofsheet steel with closed bottom, the 4sides of which are lined with asilicon carbide refractory 46, and the bottom with fire-brick 41. It issupported -on a -base 42 and has a drain y43 :in the bottom,normally-closed by a plug (not shown). The lining-4tla of the lupperpart is of silicon carbide refractory or Iirebrick and tapers internallyto a neck 44, closed by -a `removable lplug 45. The lining 40a isextended on one side to accommodate a trough 46 forming a continuationof trough 35 (Figures 2 and 5) and on the opposite side to accommodate atrough d communicating with the 'Zinc-collector 14 (see Figures y'1 and2), the latterbeinga rectangular Apot made of any suitable refractorymaterial, and .having means (not shown) for tapping off the contents.

The trough 46 is lprolonged by an arcuate trough 47 (see Figure 9) fromthe ends of which two channels 48 extend downwardly in the .mass o-f thelininglitla termi- -nating in openings 49 (Figure 7) in the interior ofthe chamber enclosed by the lining 4t), 40a.

The trough Si) is deepend at its inner end 'to form -a well 56a and isextended beneath a hanging Wall 51, whose lower edge is below the level`of the floor ,of the trough Si), to form a channel 52 in the lining 40aterminating at an internal opening 53 just below the neck 44.

In the vertical plane at right angles to the centre line of the troughs46, 50 (Figures 8 and 10) the lining 40, 40a is extended inwardly toform a vertical internal rib 54 supported on an angle section beam 55and bracket 55a and enclosing the upper part of a vertical steel pipe56, which is bonded into the rib S4 by means of hooks 57 andextends fromabove the top of the separator, where it is closed by a cover 5S, tonear the bottom of the separator, its lower end being open. A horizontalpipe Y59 branches from pipe 56 at a slightly lower level than the oorsof troughs 46, 50 and is connected to the pipe 3S, hereinbeforementioned (see Figures 2, 3).

The upper part of the shell 39 is surroundedbyasheet metal jacket 60having an inlet 61 and an outlet 62wl1ere- 6 by cooling air iscirculated vthrough the jacket. A similar sheet metal jacket 63 withinlet 64 and outlet 65 lserves for circulating heated air rrund thelower part of the shell 39.

The blast furnace gases containing Zinc-vapour (Figures 1 and 2)passfrom the furnace outlet i5' through passage 116, without sensibleloss of temperature, into the condenser compartment 18 where they meet'ashower of molten lead thrown up by the rotor 22 and are therebyshockchilled so that a part .of their zinc-vapour content is condensedand dissolved by the molten lead without serious oxidation or theformation of obnoxious quantities of blue-powder. The gases, stillcontaining some zincvapour, then pass through opening 21 intocompartment 19 to meet a second shower `of molten lead thrown .up byrotor 23, whereby further ,condensation and solution of zinc is eected.The gases, now substantially stripped of Zinc-vapour, finally leave thecondenser by the outlet 26, uptake 27' and downwardly extending pipe 2Sto enter the gas-cleaning apparatus.

Molten lead continuously enters lthe compartment 119 through pipe 3&5and leaves 'this compartment, after dissolving some Zinc, oy way ofchannel 31 to enter compartment 1S, in which it dissolves more zinc.Some yof the lead thrown up by 'the rotor Z2 in this compartment fallsinto the elevated trough 32, whence it runs through opening 33, well 34,'opening 36 Vand troug 35 into the trough 46 yof the zinc-separator 13the openings 33 and 36 being drowned. Any 4overliow from trough V32escapes 1over 'the lower of its walls back into compartment lid. Thehanging 'wall ,constituted b y the part of partition 2t? above theopening 2li ensures that no large yamount `of lead is splashed directlyinto trough 32 from compartment 19, having regard to the direction of"rotation of rotor 23.

The'zincy-lea'd received by trough 46 (Figure \9) ows into arcuatetrough 47 and down through the channels 4S and openings 49 `into thechamber of the separator, While molten lead from the bottom of the'separator containing `a smaller amount of dissolved zinc flows up pipe56 (Figure 2) and out through pipe 59 toenter compartment V19 of thecondenser bypipe '38.

The upper part of the separator chamber (Figures -8 vand 10) is cooledby the air flowing through jackets 60, causing some of the zinc Vtoseparate from Athe molten lead asa zinc-rich alloy containing a smallamount only of lead and to 'oat on the top of the body of lead in the.separator chamber, the level of the face of separation being indicated(Figure I8) by dotted line 69, which is above the openings 49 ofchannels 48. Cooling of the zncy lead in the well 34 and trough 35,leading to premature separation of zinc, is minimised by roofing thewell and trough as 'previously described.

The separated zinc ows out (Figure 7) by openings '53, channel v52, well50a and trough 59 into the zinccollector 14 (Figure 2), the hanging wall51 (Figure 7) providing an air seal for the interior of theseparatorchamber.

The levels of molten metal in the trough 46, andv neck 44 .and in trough50 are indicated by dotted lines 66, and 67, respectively (Figure 7),and the level of molten lead in the pipe 59 by dotted line 68 (Figure8). 'Ihe trough 50 terminates in a spout delivering into the collector14 and the level of the floor of trough 50 determines the level 67within narrow limits depending yon the rate of flow in the trough 50,the width of the trough being great enough to enable a -shailow streamof molten metal to maintain the required flow-rate, whereby variationsof the level 67 due to variations of How-rate, being expressibleasfractions of the mean depth Aofthe stream, are minimised. The verticaldistance bei tween levels 67 and y68 determines the depth of the zinclayer from level 67 to the separation level 69 in 'accordance withelementary hydrostatic principles, having regard to the density ratio ofthe two liquids, viz. lead saturated with zinc and zincsaturated withlead, at

the temperature of the upper part of the separator chamber.

The circulation is maintained by gravity owing to the head provided bythe difference between the level 66 of the zincy-lead in the trough 46,which is determined by its level (Figure 1) in trough 32, and the level63 of the lead in pipe 59, there being no great ditierence of densitybetween the liquid iilling channels 48 and in trough 47, 46 and thatfilling pipe 56 and in pipe 59.

The channels 48 are inclined so as to give the zincylead flowing downthem a tangential entry into the separator-chamber, thus assisting evendistribution of flow down the chamber.

The jacket 63 is thermostatically controlled to maintain a predeterminedtemperature-say 450 C.-higher than the melting point of zinc saturatedwith lead, viz. 418 C., in the lower part of the separator chamber.Zincy-lead enters the chamber through openings 49 at a highertemperature. Its excess heat is extracted by the cooling air circulatedthrough jacket 60 thus maintaining the upper part of the chamber atsubstantially the same temperature as the lower part, any tendency forthe upper part to be cooled below the temperature maintained in thelower part being prevented by convection.

The percentage of zinc separated from the lead in the separatorrepresents the diiierence between the zinc concentration in the leadleaving the outlet 33 of the condenser compartment 18 and that in leadsaturated with zinc at the temperature of the separator 13. The leadleaving the condenser is not usually saturated with zinc.

Lead enters the condenser compartment 19 from the separator 13 at theseparator temperature-say 450 C. As it passes through the condenser incounter-current to the furnace gases, condensing zinc-vapour as it goes,it receives the heat of condensation and takes up heat from thenon-condensable gases and its temperature therefore rises, thetemperatures of the compartments 18, 19 being regulated, e. g. byadjusting the amount of external lagging, which may be provided byremovable refractory blocks (not shown), so that the lead leaves thecompartment 19 by passage 31 at a temperature between 450 C. and 500 C.and leaves compartment 18 by the trough 32 and well 34 at a temperaturebetween 550 C. and 620 C.

It will be evident that no zinc can be separated until the lead has beenrecirculated through the condenser and separator until the body of leadin the separator is saturated with zinc at the temperature at which theseparator is maintained. At 418 C. the zinc-concentration in this bodyof lead is about 1.7% and at 450 C. about 2.2%. Once this concentrationhas been attained any further zinc condensed from the furnace gases isseparated substantially completely and recovered in the collector 14.

The eiiiciency of extraction then equals the eiciency of condensation,and this depends on (a) the temperature at which the furnace gases leavethe condenser, which, ideally is little above the temperature of thelead bath in the second condensing zone 19, and (b) the concentration ofzinc-vapour in the gases entering the first condensing zone 18. Thefirst factor (a) determines the partial pressure of zinc-vapour in thegases leaving the second condensing zone and hence the zincvapourconcentration in the spent gases. The condensation eiciency is measuredby the difference between the initial and final ratios of zinc-vapour toinert gas divided by the initial ratio. It the temperature (a) is 450C., the partial pressure of zinc-vapour over lead is approximately 0.36mm. Hg, and the corresponding concentration in the spent gases is0.047%; if the initial concentration in the furnace gases is the idealcondensation eiciency is just over 99%, being given by the equation:

Eioleney (percent) 100 X 5/9 5 In practice, of course, it is bound to besomewhat lower, but by suitably matching the mass-iiow-rates of thefurnace gases and of the circulation of molten lead in a condenser andseparator whose capacities are suitably matched to that of the furnace,a close approach to the ideal eciency may be achieved.

In a plant as described above the rate at which lead is circulated isabout times the rate or zinc production, by weight, e. g. for a zincoutput of 10 tons per diem, the lead circulation would be about 1000tons per diem. The total Weight of lead in the circuit is not critical,but in a plant having an output of 10 tons of zinc per diem about 70tons would be a suitable figure for the total amount of lead in thecircuit.

The process as above described may be modified and simplified by usingsingle-stage condensation in which case the apparatus is similar, butmodified as shown in Figures ll and 12, the second condenser compartment19 and rotor 23 of Figures l to 3 being omitted and the pipe 33, whichis connected with the pipe 59 of the separator 13, communicating with anopening 37a in the bottom of compartment 18, while the gas outlet 26a,corresponding to outlet 26 of Figures 1 and 3 is located above thetrough 32 in compartment 1S (see Figure la).

Wit-h single-stage condensation the temperature of the compartment 18 isregulated so that the lead leaving it by trough 32 and well 34 has atemperature between 500 C. and 550 C., the process being otherwise aspreviously described.

We claim:

l. In apparatus for producing zinc from a gaseous zinc vapor mixtureobtained from a Zinc smelting furnace, the improvement comprising acondenser with a confined condensing chamber, a sump at the bottom ofthe condenser for holding a circulating body of molten condensing metaland collecting condensed zinc therein, a gas inlet at one side of thechamber above the sump for the passage of the gaseous mixture from thesmelting furnace to the condensing chamber, a gas outlet at the oppositeside of the chamber above the sump for the escape of spent gases, amolten metal inlet to the sump for the entrance of the molten condensingmetal, an elevated trough extending at least in part across the chamberabove the sump, means in the chamber for elevating molten zinc-enrichedmetal from the sump to the trough, and a molten metal outlet at thetrough for the passage from the chamber of the elevated moltenzinc-enriched metal under hydrostatic-head.

2. Apparatus according to claim 1, in which the means for elevating themolten zinc-enriched metal includes a splash rotor disposed in part inthe sump and in part in the space above the sump adjacent the elevatedtrough, said rotor being rotatable in a direction to splash moltenZinc-enriched metal from the sump into the trough.

3. Apparatus according to claim l, in which the means for elevating themolten Zinc-enriched metal includes a horizontally disposed splash rotordisposed in part in the sump and in part in the space above the sumpadjacent the elevated trough, said rotor being rotatable in a directionto splash molten Zinc-enriched metal from the sump into the trough.

4. Apparatus according to claim 1, in which the molten metal outlet atthe trough connects with a separator for separating zinc from the moltenzinc-enriched metal.

5. Apparatus according to claim l, in which the molten metal outlet atthe trough connects with a separator for separating Zinc from the moltenzinc-enriched metal, and a molten metal outlet connects the separatorwith the molten metal inlet to the sump.

6. Apparatus according to claim 1, in which the molten metal outlet atthe trough connects with a separator for Separating zinc from the moltenzinc-enriched metal, and a molten metal outlet connects the separatorwith the molten metal inlet to the sump on substantially the same levelso that a continuous stream of molten condensing metal may llow bygravity from the separator to the sump of the condenser.

7. Apparatus according to claim 1, in which a lower smaller sump dependsfrom the first sump, and the means for elevating the moltenzinc-enriched metal includes a splash rotor disposed in part in thelower and upper sumps and in part in the space above the upper sumpadjacent the elevated trough.

8. Apparatus according to claim l, in which the condenser is dividedinto at least two condensing chambers, each chamber having its own sump;the sumps and the chambers are separated from each other by a foot-wallextending at least in part between them; the elevated trough is disposedin the first chamber, adjacent the furnace; a molten metal passagewayconnects the sumps so that molten zinc-enriched metal may flow from thesecond sump to the first sump by gravity; the gas inlet for the gaseousmixture connects the first chamber; a gas passageway above the foot-wallconnects the chambers so that partially spent gaseous mixture may passfrom the rst chamber to the second chamber; the gas outlet for the spentgases connects the last chamber; the elevating means is disposed in therst chamber for elevating molten zinc-enriched metal from its sump tothe trough; and the molten metal inlet for the entrance of the moltencondensing metal connects the sump of the second chamber.

9. Apparatus according to claim 8, in which a hanging-wall depends fromthe top of the condenser between the two chambers and above thefoot-wall to separate the chambers and to define the gas passagewaybetween them.

10. Apparatus according to claim 8, in which the means for elevating themolten zinc-enriched metal includes a splash rotor disposed in part inthe Sump of the first chamber and in part in the space above the sumpadjacent the elevated trough, said rotor being rotatable in a directionto splash molten zinc-enriched metal from the latter sump into thetrough.

11. Apparatus according to claim 8, in which the means for elevating themolten zinc-enriched metal includes a horizontally disposed splash rotordisposed in part inthe sump of the first chamber and in part in thespace above the sump adjacent the elevated trough, said rotor beingrotatable in a direction to splash molten zinc-enriched metal from thelatter sump into the trough.

l2. Apparatus :according to claim 8, in which the molten metal outletfat the trough connects with a separator for separating Zinc from themolten Zinc-enriched metal.

13. Apparatus according to claim 8, in which the molten metal outlet atthe trough connects with 'a separator for separating Zinc from themolten zinc-enriched metal, and #a molten metal outlet connects theseparator with the molten metal inlet to thesump of the second chamber.

i4. Apparatus according to claim 8, in which kthe molten metal outlet atthe trough connects with a separator forV separating zinc from themolten zinc-enriched metal, yand a molten metal outlet from theseparator connects with the molten metal inlet to the sump of the secondchamber on substantially the same level so that a continuous stream ofmolten condensing metal may tlow by gravity from the separator to thelatter sump.

l5. Apparatus according to claim 8, in which a lower smaller sumpdepends from the sump of the rst chamber, land the means for elevatingthe molten zinc-enriched metal includes a splash rotor disposed in partin the lower and upper sumps and in part in the space above the uppersump adjacent the elevated trough, said rotor being rotatable in adirection to splash molten zinc-enriched metal from the latter sumpsinto the trough.

16. Apparatus according to claim 8, in which a splash rotor is disposedin part in the `sump of the second chamber and in part in the space`above the sump, said rotor being rotatable in la direction to spl-ashmolten zinc-enriched metal from the latter sump in a direction generallyaway from the trough.

17. Apparatus according to claim 8, in which a lower smaller sumpdepends from the sump of the second chamber, and a splash rotor isdisposed in part in the latter lower and upper sumps and in part in thespace :above the upper sump, saidv rotor being rotatable in a directionto splash molten zinc-enriched metal from the latter sump in a directiongenerally away from the trough.

References Cited in the le of this patent UNITED STATES PATENTS

1. IN APPARATUS FOR PRODUCING ZINC FROM A GASEOUS ZINC VAPOR MIXTUREOBTAINED FROM A ZINC SMELTING FURNACE, THE IMPROVEMENT COMPRISING ACONDENSER WITH A CONFINED CONDENSING CHAMBER, A SUMP AT THE BOTTOM OFTHE CONDENSER FOR HOLDING A CIRCULATING BODY OF MOLTEN CONDENSING METALAND COLLECTING CONDENSED ZINC THEREIN, A GAS INLET AT ONE SIDE OF THECHAMBER ABOVE THE SUMP FOR THE PASSAGE OF THE GASEOUS MIXTURE FROM THESMELTING FURNACE TO THE CONDENSING CHAMBER, A GAS OUTLET AT THE OPPOSITESIDE OF THE CHAMBER ABOVE THE SUMP FOR THE ESCAPE OF SPENT GASES, AMOLTEN METAL INTEL TO THE SUMP FOR THE ENTRANCE OF THE MOLTEN CONDENSINGMETAL, AND ELEVATED TROUGH EXTENDING AT LEAST IN PART ACROSS THE CHAMBER